Fatty acids are widely used as intermediates for foods, such as monoacylglycerol and diacylglycerol, and as additives and intermediates for a variety of industrial products. Such fatty acids are obtained as a decomposed fatty acid composition by hydrolyzing vegetable oils such as rapeseed oil and soybean oil, and animal fats such as beef tallow, and then used as a fatty acid composition.
However, the fatty acid composition produced by simply hydrolyzing the animal or vegetable fats or oils having the intact fatty acid composition as mentioned above is not necessarily suitable for industrial raw material. Thus, it is necessary to prepare the desired fatty acid composition, for example, containing low trans unsaturated fatty acid or low unsaturated fatty acid, depending on the purpose of utilization.
As a fractionation method of the fatty acid composition, compression, solvent fractionation, spontaneous fractionation (dry fractionation), and wetting agent fractionation are known. Among them, spontaneous fractionation and wetting agent fractionation are preferred from the viewpoint of separation efficiency, safety and economic performance.
Generally, the wetting agent fractionation is applied to the fatty acid composition which contains a large amount of saturated fatty acid originated from beef tallow or palm kernel oil, because a large amount of solid portion (crystals of saturated fatty acid) is formed by cooling (Patent Documents 1 to 4). On the other hand, the spontaneous fractionation is applied to the fatty acid composition which contains relatively low amount of saturated fatty acid, because smaller amount of solid portion is formed by cooling and the amount to be treated is small (Patent Document 5).